Methods: :
Six weeks old albino Sprague-Dawley rats were the experimentalanimals. All animals were anesthetized with ketamine/xylazine,95/14 mg/kg body weight, 20 min prior to exposure and the pupilsof both eyes were dilated with tropicamide 10 mg/ml. In thefirst experiment, 12 animals were divided into four exposuretime groups of three animals, 25, 64, 169 and 400 s. In eachanimal, one of the eyes was exposed to a 3 mm in diameter spot,with quasi top hat spatial distribution of 6.2 W, 1090 nm generatedwith a CW fiber laser (Model SP-120C, SPI Lasers, UK). The animalswere sacrificed 24 hrs after exposure and the lenses were isolatedfor macroscopic imaging in dark-field illumination and measurementof intensity of forward light scattering. In the second experiment,the same power of the laser, 6.2 W, and the same exposure condition,was used but with the exposure time set to 8 s. Altogether,16 animals were exposed unilaterally and then sacrificed at6, 18, 55 or 168 hrs after the exposure. The lenses were thenisolated for macroscopic imaging in dark-field illuminationand measurement of intensity of forward light scattering.

Results: :
In the first experiment, if was found that the difference ofintensity of light scattering induced between the exposed andthe contralateral eye increased as a function of exposure timeand that the increase can be approximated with a 2nd order polynomialwithout 0 and first order term, CIk(0.95) = 0.18 ± 0.0004rel. units/s (d.f. 11). Exposure times above 8 s induced a signaljust above noise. In the second experiment, it was found thatthe light scattering induced increases exponentially decliningas a function of time after exposure (1/k=75 hrs).

Conclusions: :
In vivo exposure to near infrared radiation that induces justabove detectable light scattering in the lens is associatedwith a delayed onset of light scattering. This finding indicatesthat there may be a photochemical effect of infrared radiationand thus a cumulative effect of sub threshold exposures to e.g.LEDs in remote controls and sensing devices.